1. Field
The field relates to a pixel and an organic light emitting display using the same, and more specifically to a pixel for simplifying a configuration, and an organic light emitting display using the same.
2. Description of the Related Technology
In recent years, there have been may attempts to develop various flat panel displays with reduced weight and volume compared with a cathode ray tube, which are problematic in the cathode ray tube. Flat panel displays includes a liquid crystal display, a field emission display, a plasma display panel, an organic light emitting display, etc.
Amongst flat panel display devices, the organic light emitting display displays an image using an organic light emitting diode which generates light by means of recombination of electrons and holes. Such an organic light emitting display has an advantage that it has a rapid response time and may be also driven with a low consumption power.
FIG. 1 is a circuit view showing a pixel 4 of a conventional organic light emitting display.
Referring to FIG. 1, the pixel 4 of the conventional organic light emitting display includes an organic light emitting diode (OLED), and a pixel circuit 2 connected to a data line (Dm) and a scan line (Sn) to control the organic light emitting diode (OLED).
An anode electrode of the organic light emitting diode (OLED) is connected to the pixel circuit 2, and a cathode electrode is connected to a second power source (ELVSS). Such an organic light emitting diode (OLED) generates the light having a luminance corresponding to an electric current supplied to the organic light emitting diode (OLED) by the pixel circuit 2.
The pixel circuit 2 controls current supplied to the organic light emitting diode (OLED) to correspond to a data signal supplied to the data line (Dm) when a scan signal is supplied to the scan line (Sn). For this purpose, the pixel circuit 2 includes a second transistor (M2) and a third transistor (M3) connected between a first power source (ELVDD) and the organic light emitting diode (OLED); a first transistor (M1) connected to the second transistor (M2), the data line (Dm) and the scan line (Sn); and a storage capacitor (Cst) connected between a gate electrode and a first electrode of the second transistor (M2).
The gate electrode of the first transistor (M1) is connected to the scan line (Sn), and the first electrode is connected to the data line (Dm). And, the second electrode of the first transistor (M1) is connected to one side terminal of the storage capacitor (Cst). Here, the first electrode is one of a source electrode and a drain electrode, and the second electrode is an electrode different to the first electrode. For example, a second electrode is a drain electrode if the first electrode is a source electrode. The first transistor (M1) connected to the scan line (Sn) and the data line (Dm) is turned on when a scan signal is supplied to the scan line (Sn), thereby supplying a data signal, supplied on the data line (Dm), to the storage capacitor (Cst). The storage capacitor (Cst) then stores a voltage corresponding to the data signal.
The gate electrode of the second transistor (M2) is connected to one side terminal of the storage capacitor (Cst), and the first electrode is connected to the other side terminal of the storage capacitor (Cst) and the first power source (ELVDD). And the second electrode of the second transistor (M2) is connected to the anode electrode of the organic light emitting diode (OLED). Such a second transistor (M2) controls a current to correspond to a voltage value stored in the storage capacitor (Cst), wherein the controlled current flows from the first power source (ELVDD) through the organic light emitting diode (OLED) to the second power source (ELVSS). In response, the organic light emitting diode (OLED) generates light corresponding to the current flowing therethrough.
A first electrode of the third transistor (M3) is connected to the second electrode of the second transistor (M2), and a second electrode is connected to the anode electrode of the organic light emitting diode (OLED). And a gate electrode of the third transistor (M3) is connected to the light emitting control lines (En). The third transistor (M3) controls timing of the electric current to the organic light emitting diode (OLED) according to a light emitting control signal supplied to the light emitting control lines (En).
The conventional organic light emitting display is driven in an analog driving mode. In other words, a voltage stored in the storage capacitor (Cst) may be used to display various grey levels. However, it is difficult to display an image having a uniform luminance in a panel due to the variation in a threshold voltage of the second transistor (M2) (a drive transistor) if the voltage stored in the storage capacitor (Cst) is used to display various grey levels. Also, the pixel as shown in FIG. 1 has a problem that it further includes a transistor (M3) for controlling supply time of the electric current supplied to the organic light emitting diode (OLED).